FR2659807A1 - CONTROL DEVICE FOR AN INDUCTION MOTOR. - Google Patents

Abstract

The invention relates to a control device for an induction motor. This device comprises a variable voltage and variable frequency inverter (4) for converting a direct current into an alternating current; an induction motor (5) controlled by said inverter; means (13) for controlling the slip frequency so that the current of said induction motor becomes constant; means (15, 16, 17) for executing a command so as to produce a voltage proportional to the frequency of the inverter; and means (14) for correcting the voltage proportional to the frequency of the inverter, as a function of an internal impedance angle of said induction motor. Application in particular to an induction motor controlled by means of an inverter.

Description

The present invention relates to a device

  making it possible to obtain a constant torque characteristic in a control for an induction motor controlled by

an inverter.

  FIG. 7, appended to the present application, is a block diagram of the conventional control device for an electric locomotive of the type comprising an induction motor. A current supplied from a pantograph.

  1 is introduced via a filament reactance

  trage 2 and a filtering capacitor 3, in a

  their 4 variable voltage and variable frequency, which pro-

  a variable voltage and frequency alternating current

  variable (which will be referred to hereafter as VVVF) A three-phase alternating current produced by

  the VVVF 4 inverter is sent to a three-phase induction motor.

  phased 5 to drive it A current detected by a detection

  current transformer 6 is sent to a circuit 7 for calculating the

  current, in which an IM current of the motor is calculated.

  A comparator 9 compares the current IM of the motor

  to a current control of the motor Ip produced by a dis-

  positive pilot control 8, and a gap AI between IM and Ip is sent to an amplifier 10, which, in turn, delivers a sliding frequency Fs On the other hand, the output signal of a speed detector 11 is sent to a circuit

  12 calculating the speed to obtain a frequency of

  Motor rotation frequency FR The slip frequency

  FS and the motor rotation frequency FR are added

  born in an adder 13 so as to provide a frequency

  IINV of the inverter (When operating in

  and regeneration, the values Fs and FR are subtracted from each other) The FINV frequency of

  the inverter is sent to a circuit 14 for calculating the voltage.

  which, in turn, delivers a voltage V of the motor

  part of the FINV frequency of the UPS Vue à par-

  firing of the inverter 4, the voltage V of the motor is a

  In reality, a modula-

  This is sent to a pulse modulator in duration of the inverter 4.

  modulated according to a pulse modulation in duration

  the FINV frequency of the inverter and the voltage V

of the motor.

  With the arrangement indicated above, since the voltage / frequency ratio (V / F) is controlled so as to be constant and the current is controlled so as to be constant with a reduction of

  sliding frequency Fs, we obtain a constant torque.

  This system is referred to as a control system

the frequency Fs.

  In the FS frequency control system,

  there is a problem that the couple decreases

  naked in a low frequency range.

  We will describe below in more detail

  a cause of torque reduction.

  According to a report presented in the Technical & Research Report (Part II) of the Institute of Electrical Engineers of Japan, N0109, (April 1981), page 39, the

  compensation of the voltage drop in a primary impedance

  mayor, which is the cause of the reduction of the couple in a

  range of low speeds of an induction motor, is

  by means of a V / F ratio correction in the sense that this V / F ratio increases more substantially than in a straight line, along which the

V / F ratio remains constant.

  In the prior art, in the event that the de-

  tection of the flux in the air gap of an induction motor is difficult, one chooses a line or curve of variation of the ratio of the voltage at the terminals to the frequency (V / F) which provides a couple approximately constant Indeed,

  given that it is difficult to measure the torque of the

  it is not possible to determine the V / F ratio which makes it possible to obtain, in an ideal manner, a

constant torque.

  For example, when applying the method indicated above to a rail electric vehicle, there is no significant problem even if the couple

  is not maintained at a strictly constant value

  during, for example, during activation according to a

  ascending in the case of a curve with a

  steep, the reduction of the torque poses a problem concerning the operation of the electric railway vehicle since a couple in a range of

  low speeds is required for activation.

  Similarly, in an electric locomotive using

  a control of the frequency FS, the reduction (or the vari-

  torque) has a significant influence on activation, particularly in the case where heavily loaded goods wagons are coupled together. In the case where the torque is low, activation becomes possible. correct correction

  between the production of a torque greater than a couple

  quis or desired, it appears a slip leading to the

difficulty of activation.

  An object of the present invention is to provide

  a control device for an induction motor, which would be able to provide a torque characteristic

substantially constant.

  For this purpose, in accordance with the present invention,

  tion, a frequency control system FS is equipped

  means for correcting a proportional voltage

  the frequency of the inverter according to the angle

  internal impedance of an induction motor.

  We will briefly mention here the reason why a constant torque is obtained using the correction means indicated above, but this will be described in more detail below. If we draw there curve of the value of the sine of the angle of internal impedance of the induction motor and a curve of the torque on the same graph by taking the frequency of the inverter in the abscissa, the two curves vary substantially to the same degree This advantage is taken advantage of because it is not possible to measure the torque directly In reality, the voltage is increased (or reduced) depending on the impedance angle (or its

  sinus), which keeps the torque constant.

  More specifically, the invention relates to a

  control device for an induction motor, characterized

rised in that it comprises:

  an inverter with variable voltage and frequency

  to convert a direct current into a current

ternatif;

  an induction motor controlled by said

their;

  means for controlling the slip frequency

  in such a way that the current of said induction motor becomes constant; means for executing a command so as to produce a voltage proportional to the frequency of the inverter; and

  means for correcting the proportional tension

  the frequency of the inverter, according to an angle

  internal impedance of said induction motor.

  Other features and advantages of the pre-

  invention will emerge from the description given below.

  after reference is made to the accompanying drawings, in which like reference numerals denote similar parts in the various views of the subject of the invention and in which: FIG. 1 represents a block diagram showing an embodiment of the invention; present invention; Fig. 2 is a block diagram showing an example of a calculation circuit of the correction factor according to the present invention; Fig. 3 is a diagram showing another example of a calculation circuit of the correction factor according to the present invention; Fig. 4 is a block diagram of another embodiment of the present invention;

  FIG. 5 represents a diagram representing

  both the calculation circuit V / F profile, according to the present invention;

  Figure 6 is a graph showing a

  FINV-Kl, for which the frequency of

  is taken as a parameter; Figure 7, which has already been mentioned, shows a block diagram of the conventional speed control system;

  FIG. 8 represents an equivalent T circuit.

slow of an induction motor;

  Figure 9 is a graph showing the character of

  the torque versus the frequency in a control system of the frequency Fs;

  Figure 10 is a graph showing the

  characteristic of variation of the power factor and the sinus of the impedance angle as a function of the frequency; Fig. 11 is a block diagram of the conventional voltage control system Vc;

  Figure 12 is a graph showing the

  torque variation as a function of the time

  in a voltage control system Vc;

  Figure 13 is a graph showing the

  torque in the case of switching between control systems; Figure 14 is a block diagram of another

  embodiment of the present invention, which introduces

  causes switching between control systems; Fig. 15 is a block diagram of another embodiment of the present invention, which implements switching between control systems; Fig. 16 is a block diagram of another embodiment of the present invention, which implements switching between control systems;

  Figure 17 is a graph showing the

  riation of voltage as a function of temperature; and Figure 18 is a graph showing the effect

  of a circuit producing a time constant or a cir-

cooked by delay.

  The following will be described in detail below:

  invention with reference to the accompanying drawings.

  Before explaining the embodiments, we will indicate in detail the principle of the present

invention.

  In FIG. 8, a T-circuit is shown

  equivalent of an induction motor

  v, designates an input phase voltage, I a

  input, X 1 a primary reactance, Ri a primary resistance, Roo the losses in the iron, X 00 an excitation reactance, X 2 an equivalent secondary reactance, R 2 / S

  equivalent secondary resistance (S: slip rate

  I 2 a secondary current (for a reduced primary value) and Io a composite current of a circuit

  of excitation and a circuit of losses in the iron.

  If a primary impedance Zl, an impedance

  Z 2 and an impedance ZO for the excitation and the losses in the iron are represented by Z 1 = Ri + jx 1, (1) Z 2 = R 2 / S + j X 2 (2) Zo = Ro + j XO (3)

  and solve the equations of the circuit established according to

  to Kirchhoff's law, we obtain the following Z 2

IO = V (4)

Z O l + +

Z O Z 1 + Z 1 Z 2 + Z 2 ZQ

o O

I 2 = V (5)

Z O Z 1 + Z 1 Z 2 + Z 2 Z O

Z O + Z 2

I 1 V (6)

ZOZ 1 + Z 1 Z 2 + Z 2 Z O

  Similarly, a secondary input power P 2 and a torque TRQ are represented by the following equations R 2 P 2 2 = 2 m lWl (7) S

P 2

  TRQ = -lN ml (8) 27 r FINV () Pole 12 representing the absolute value of I 2, FINV is the frequency of the inverter, Pole the number of pairs of

poles, and m the number of phases.

  We try to simulate the characteristics of an induction motor using the equations above We can know the torque TRU and the current I if we know or if we determine the frequency FINV of the inverter, the frequency slip Fs, the voltage V and

  the constants (R 0, R 1, R 2, X 0, X 1 and X 2) of the motor.

  In the case where a control system of the

  Vc, in which the modulation rate is controlled from

  in order to make the motor current constant, the frequency

  slip rate Fs is fixed. Therefore, if we de-

  end of the motor rotation frequency, it is possible to

  frequency of the inverter, and the impedance of the equivalent circuit (or

  The result of this is that it is determined

  a simple tension at the moment of the appearance of a cou-

  Therefore, we can execute

simple simulation.

  However, in the case of the frequency control system Fs, mentioned with reference to FIG. 7, it is not possible to execute the simulation, contrary to the case of the control system of the voltage VC, since the

  sliding frequency Fs varies according to a variation

  This is due to the fact that the current I

  comes a function of the sliding frequency Fs and

  the voltage E, as is apparent from equations (4) to (6).

  Even if we reduce the current I so that it is only

  As a function of the slip frequency FS by introducing the condition that the voltage V is proportional to the frequency FINV of the inverter, a higher order equation is obtained and it is difficult.

to solve this equation.

  In this case, since it is desirable to calculate and determine the characteristics when the frequency FR of the motor reaches a certain value, it is possible to determine the frequency FINV of the inverter if the slip frequency Fs to be determined is fixed. As the FINV frequency of the inverter and the voltage V are proportional to each other, the voltage V can be calculated.

  I is constant, we can determine the frequency of

  using the following asymptotic method:

  (1) A possible range of frequencies is subdivided

  slip, which ranges from the maximum value to

  the minimum value, for example five parts and

  flows current I for the respective parts.

  (2) Since current I has a

  their constant, a range situated between two values of the

  The result of the calculation covering the constant current value is subdivided equally into five parts and the

  Current I is calculated on the basis of the slip frequency

  ment. (3) The operation carried out in (2) is continued until the error between the value of the current I obtained in (2) and the constant value becomes equal or

  less than a value of the order of 10-6.

  The slip frequency FS at this moment is

  obtained by means of the preceding calculation circuit The result

  state of simulation in a frequency control system.

  FS, based on this technique, is shown

  in Figure 9 From the result shown in the figure

  gure 9, we see that the real pair TRQ differs from a couple

  TRQO, notwithstanding the fact that the current I and the ratio

  port V / F from the voltage to the frequency are controlled from

  If this situation persists, it is difficult to obtain constant torque control by means of

of the reaction of the current.

  This reduction in torque is caused by a large variation in the distribution ratio of currents Io and I 2 between a range of high speeds and a range of low speeds (see the equivalent circuit in FIG. 8). The authors of this report have investigated the characteristic of variation, as a function of frequency, of an internal impedance, which is a cause of the variation of the subdivision rate. In this respect, the impedance angle p can be calculated from the relation (6) Using this impedance angle A, sin <p and cos <p (or power factor) and a torque variation curve are shown on the same graph (see Figure 10). 10, it turns out that the reduction of the torque in a range of low speeds and the curve giving sin p are similar to one another. The height at the base of the present invention is aimed at obtaining a constant torque characteristic by taking advantage of the

done previously.

  To obtain a torque characteristic

  constant, it is better to calculate a couple and

  but a couple calculated from relations (7) and (8) is as follows: I 22 R 2 m

TRQ = (9)

27 FINV

  () s Pole Indeed, since the secondary current

  I 2 can not be measured, it is not possible to calculate

ler the couple.

  However, it is possible to calculate the impedance angle <in the case where the motor rotation frequency FR and the slip frequency Fs are known. The equations for the calculation of the impedance angle g are as follows:

FINV = FR + FS (10)

  w = 27 r FI Nv (11) X 00 = w L 00 oo, X 1 = w L 1, X 2 = w L 2 (12) FS

S = (13)

  FINV R 2 FI Nv Z 2 + j L 2 = R 2 + ji L 2 (14) S Fs and, from relations (1), (2), (3) and (4), we obtain Oil + Z 1 Z 2 + Z 2 ZO z = = R + jx (15) Zo + Z 2 X x <= arctg () (16)

R

  Since sin p thus determined resembles the curve il of the torque, the value of sin p can be considered as a torque Si increases the motor voltage as a function of the decrease rate of sin <(= 21 (power factor) 2) from a nominal value sin go, it is possible to correspondingly increase the torque so as to obtain a

  Constant torque characteristic.

  Hereinafter, mention will be made of a method for adjusting

the engine voltage.

  Provided that V O and Fo represent a voltage no

  a nominal frequency in the case where the internal constants of an engine are set, a value of

  reference of V / F is VO / Fo In this case, V O and Fo represent

  voltage and frequency at a transition point from a variable voltage variable frequency range (or VVVF region) of an inverter to a constant voltage, variable frequency range (or CVVF region) of the inverter. that the impedance angle at this instant is <p, the motor voltage V is adjusted for any FINV frequency of the inverter in a range of low speeds as follows FINV sin g OV xx VO (17) Indeed, a constant torque characteristic is obtained by multiplying the value V / F conventionally used by a correction factor equal to sin in the conditions where the current is constant. The result of

  the simulation for a TRQ torque after correction is

  shown in FIG. 10 In this figure, it can be seen that if the current I is constant, the torque is substantially constant.

  We will now explain a form of realization

  of the present invention with reference to FIG.

  We will not repeat here the explanation given

  previously with reference to FIG. 7 and we will describe

  detailed way the differences with respect to this figure.

  The newly added components to the device represent

  7 are a circuit 14 for calculating the

  correction processor, a generator 15 of the V / F ratio of

  and multipliers 16 and 17.

  The circuit 14 for calculating the correction factors

  It receives the motor rotation frequency FR and the slip frequency FS so as to calculate a correction factor K 1 for a value V / F, for a frequency FINV of the inverter, at which the inverter 4 operates. 'we have FINV <For the circuit 14 delivers K 1 having a

  value greater than 1 When FINV> Fo, the pair

  is slightly greater than a reference torque, but the error is negligible since the torque is low In the case where we could not neglect

  the error, the circuit 14 can deliver a lower value K 1

greater than 1 when FINV> Fo.

  In the multiplier 16, an output signal of the

  generator 15 of the reference value V / F, issued earlier

  in the light of the different conditions

  the characteristics of an induction motor 5 and the properties of an electric locomotive, is multiplied by the correction factor K 1. Therefore, a value V / F (= K 2) for the frequency FINV of the inverter at this time is determined The multiplier 17 multiplies the frequency FINV of the inverter by K 2, which provides a voltage V (or a modulation rate y) to obtain a constant torque. FIG. 2 shows an example of the

  circuit 14 for calculating the correction factor.

  The motor rotation frequency FR and the frequency

  FS slip are added together by adding

  neur 1401, which provides the FINV frequency of the inverter.

  This FI Ni V frequency of the inverter is sent to a calculation circuit 1403 which in turn delivers an electric angular velocity w The slip frequency Fs and the frequency FINV of the inverter are sent to a circuit 1402 for calculation. slip rate, which in turn delivers the slip rate S The slip rate S is used for the calculation of the secondary impedance Z 2 (see the relation

  (2)) The slip rate S and the angular velocity

  each circuit W is sent to a circuit 1404 for calculating the impedance angle, which in turn executes an operation according to the relationships (10) to (16) to provide an impedance angle p A circuit 1405 for calculating the factor correction divides the sin p O at a nominal time per sin

  <so as to deliver a correction factor K 1.

  Referring to the equivalent circuit shown in FIG. 8, the impedance angle p can be determined from the relationship between the voltage V and the current I. In a high speed range, a relatively accurate value can be calculated. since the frequency is high However, in a low speed range, a considerable time interval is necessary before the detection or determination of a phase difference.

  same, since the voltage V and the current I are

  once the inverter 4 has been commanded, the control sequence is delayed, resulting in a variation of the

  Therefore, in accordance with the present invention,

  the impedance angle <is not determined or calculated

  from the previous relationship.

  In the following, we will show another example of the cir-

  cooked 14 calculation of the correction factor, referring

in Figure 3.

  The slip frequency FS and the rotation frequency FR of the motor are introduced into an adder

* 1410 and are added in such a way as to provide a frequency

  the inverter ENDV, which in turn is sent to a circuit 1411 for calculating a variation profile A correction factor K 1 calculated by using the constants of the motor has been previously stored in the form of a In the example shown in FIG. 3, the correction factor K 1 in a CVVF region is less than 1. However, it can be equal to 1. Circuit 1411 for calculating the profile delivers the correction factor K 1 as a function of the frequency FINV of the inverter, delivered by the adder 1410.

  processing speed in the example shown on the

  FIG. 3 is remarkably fast compared to the processing speed involved in the example shown in FIG.

figure 2.

  Figure 4 shows another embodiment of the present invention.

  differs from the embodiment shown in FIG.

  1 in that a circuit 18 for calculating the varia-

  V / F is provided in place of the correction factor calculating circuit 14, the V / F ratio generator 15 of FIG.

  reference and multipliers 16 and 17.

  We will explain the details of the circuit 18

  V / F variation ass, with reference to FIG. 5.

  As mentioned previously, the

  correction is determined in the case where the

  In this example, the motor constants are

  the FINV frequency of the inverter is entered and a motor voltage V corresponding to the frequency of the

  the inverter is delivered (The motor voltage V is

  simplification and a modulation rate

  is actually delivered) A value corresponding to the value

  their previously calculated and multiplied by a value of the reference V / F ratio, is stored in the circuit 18

  calculation of the V / F variation profile.

  In the circuit 14 for calculating the loading factor

  rection, shown in Figure 2, the slip frequency

  Fs is introduced in order to determine the slip rate S to be used to determine the secondary impedance Z 2. In fact, the slip frequency Fs is introduced for the determination of the secondary impedance Z 2. However, in the circuit 1411 of the profile, which comprises the circuit 14 for calculating the correction factor represented in FIG.

  circuit 18 for calculating the variation profile of V / F,

  5, the slip frequency Fs is not introduced. Here, only the correction factor K 1 or the motor voltage V is obtained as a function of the frequency FINV of the inverter Referring to FIG. ,

  the sliding frequency Fs varies according to the

  of the current, with the result that

  the secondary impedance Z 2 varies accordingly.

  Therefore, it is necessary essentially to deter-

  precisely reduce the sliding frequency Fs.

  Here we will explain why

  constant torque can be obtained even by means of a

simplified thread.

  The correction factors in FIGS. 3 and 5 are determined in the manner indicated above. In fact, it is desirable that the sliding frequency Fs be fixed. Therefore, a correction factor K 1 is determined for each rotation frequency. of the motor, for fixed sliding frequency FS This can be represented graphically by the graph shown in the circuit 1411 for calculating the profiles of FIG. 3, in which the frequency FINV of the inverter and the correction factor K 1 are carried. respectively on the abscissa and on the ordinate A graph obtained by multiplying a voltage V for each frequency FINV of the inverter by the correction factor K 1 thus determined is represented in the circuit 18 of the

  calculation of the V / F profile in FIG.

  In the following, we will prove that even if the frequency

  FS is fixed, the influence is weak Figure 6 graphically shows a relationship between the FINV frequency of

  the inverter and the correction factor K 1, the slip frequency Fs being taken as a parameter. In this figure, it can be understood that, when the frequency

  slip FS is modified in relation to its nominal value

  nal (100%) to take the values 110%, 150% and 90%, a deviation of the correction factor from its value corresponds to the nominal slip value is within the limits of a tolerance. region where the frequency of the inverter is less than 2 to 4 Hz, there is almost no influence, since a VC command is performed, as will be mentioned later Therefore, if one calculates the correction K 1 with fixed FS slip frequency, it

there is almost no difference.

  The previous explanation was given for the case where the constant torque control, based on the control of the frequency Fs, is executed throughout the range of speeds. This command of the frequency FS does not allow

  not all and has a disadvantage In fact, the detection

  11, for which an encoder is used in practice, has a low resolution in a range of ultra-low speeds (from 0 to 4 Hz). If it is not possible to accurately calculate a frequency in or out of

  proximity to the range of ultra-low speeds, it appears

  for the value of the rotation frequency FR of the motor

  significant error which, in turn, is superimposed on the inverter's FINV frequency.

  the FINV frequency of the inverter is reported in the

  V, which makes it difficult to control a constant torque. Under such conditions, a method is used,

  according to which one uses, in a range of weak vi-

  tesses, a control of the VC voltage to make the

  constant by changing the modulation rate of the inverter so as to increase or decrease the voltage while setting the slip frequency Fs.

  represents a block diagram of the control system of the

  As a summary explanation, it can be said that an Ip command of the motor current sent by a pilot control device 8 and an IM current of the motor delivered by a current calculation circuit 7 are compared in a comparator 9. , which leads to a difference AI between IM and Ip, and the voltage V of the inverter is increased or reduced according to the difference AI This method has the advantage that the torque is controlled at a value substantially constant if the current is controlled to be constant, but has the disadvantage that, when the secondary resistance R 2 of the motor varies according to the temperature of the latter, the increase or reduction of R 2 causes a variation of torque, notwithstanding the fact that the current is controlled at a value

  constant This case is illustrated in Figure 12.

  We will now explain with reference to the

  13 of the considerations made in the case where

  VC voltage control and FS frequency control

are used in combination.

  It is assumed here that the control of the frequency FS is carried out by means of the use of the control system shown in FIG. 1 to obtain a torque control at a constant value, and the control of the voltage

  Vc is executed using the control system

  shown in Figure 11 provided that there is no variation

  torque when switching between the control of the voltage Vc and the control of the frequency FS when the rotor temperature of the induction motor is equal to 1100 C, the torque obtained when the rotor temperature is equal to OC is decreased As is shown in FIG. 13 In reality, when a switching is performed between the control systems during power operation, the torque has a significant variation from point A to point B. FIG. -block in the

  case an order of the frequency Fs is combined with the technique

  anterior device (described in patent JP-A-57-13989), according to which, to reduce the variation of the torque during the control of VC, a termistance is connected to the stator of the

  induction motor so that the corrected value is de-

  terminated according to the stator temperature, which

  allows to correct the slip frequency On the

  14, the same reference numbers as those used in FIGS. 1 and 11 denote the same components or elements as those shown in FIGS. 1 and 11. A part of the arrangement of FIG. 14 will be explained.

  which is different from the arrangement of Figure 1 or 11.

  In the case of the control of the voltage Vc (or at a low speed), the output signals of the sensors of

  temperature 27 sent to and in the vicinity of the motor stator.

  5 are introduced into a circuit 22 of

  calculation of the rate of change of resistance In this

  the ratio of the current temperature T to a reference temperature To is calculated, for the delivery of a correction factor K 3 A generator 23 of the frequency Fsp of

  reference produces a FSP slip frequency at the time

  reference temperature To (or a temperature at which

  a variation of the torque is not caused in the case of switching on the control of the frequency Fs, for example

  To = about 1100 C) A multiplier 24 multiplies the

  output signal FSP of the generator 23 of the reference frequency Fsp, by the correction factor K 3 and by the output signal of the circuit 22 for calculating the rate of change of the resistance, in order to deliver the result in the form of a slip frequency Fs At this time, since each of the Vc-FS switches 25 and 26 is placed on a side a (or the control side of the voltage VC, the slip frequency FS and a rotational frequency FR of the motor are added by an adder

  13 to provide the FINV frequency of the inverter.

  When a generator 21 of the Vc-Fs switching signal confirms the increase of the rotational speed or the rotation frequency FR of the induction motor 5 to a predetermined value (2 Hz to 4 Hz) due to the gradual increase of the rail electric vehicle, the Vc-FS switching signal generator 21 outputs a signal which causes the actuators of Vc-Fs 25 and 26 to operate. Each of the switches Vc-Fs 25 and 26 is switched on. side b (or control side of the frequency

  Fs), so that the system switches to control of the frequency

  Fs I mentioned above.

  The circuit 18 for calculating the V / F profile, explains

  5 with reference to FIG. 5, can be used in place of the circuit 14 for calculating the correction factor, the

  generator 15 of the reference V / S signal and multipliers

16 and 17.

  According to the present embodiment, a substantially constant torque can be obtained during a

  period from the moment of activation or start

  rage up to high speed operation, including

the switching time.

  In the following, we will explain other forms of

of the present invention.

  It is assumed that a line drawn in FIG. 17 represents the frequency-voltage characteristic in the torque and the current are constant when the induction motor rotor temperature is equal to a reference value To (for example 1100 C). Two lines in dashed lines formed respectively by the respective succession of a line and a point and by the respective succession

  in one line and two points, plotted in Figure 17,

  present respectively the characteristic frequency

  for a low temperature and for a high temperature in the case where only the temperature is changed

  under the same conditions as those used at

  As is apparent from this figure, the ratio of the voltage V to any temperature at

  a voltage VO at the reference temperature TO is sensi-

  In accordance with the calculations made by the authors of the present invention, this ratio is substantially equal to the ratio of the secondary resistance of the invention.

  induction motor at any temperature at the

  secondary resistance of the motor at the reference temperature T 0. If the preceding indications are used, it is possible to maintain the constant torque in the case of a variation making the control of the voltage VC to the

frequency control FS.

  An exemplary embodiment will be explained with reference to FIG. 15. The explanation made with reference to FIG. 14 will not be repeated. In FIG. 15, the same reference numerals as those used in FIG.

  14 designate the same components or elements as those

shown in Figure 14.

  Upon activation or startup, each of the switches 25 and 26 is placed on the side a so as to select a VC voltage control system La

  motor rotation frequency is sent to a general

  28 of the reference voltage, which in turn produces a reference voltage VC corresponding to the reference frequency FR of the motor. The reference voltage Vc delivered

  by the generator 28 of the reference voltage and a voltage

  sion V (or a modulation rate y) delivered by an amplifier

  19 are sent to a generator 29 with a correction factor, which in turn calculates K 4 = V / VC. The value of this correction factor K 4 is less than 1 in the case where the present temperature T on the secondary side of the induction motor 5 is lower than the reference temperature To or in the case where the voltage V is lower than the reference voltage VC In the case where the current temperature T

  is greater than the reference temperature TO, K 4 is su-

less than 1.

  The output signal of the generator 23 of the reference frequency FSP, which delivers a reference slip frequency Fsp for obtaining a torque to be delivered at the reference temperature TO, is

  multiplied by the correction factor K 4 in a multiplication

  24, which makes it possible to obtain a sliding frequency

FS corrected.

  For example, in the case where the temperature

  T is lower than the reference temperature TO, the torque is low. Therefore, unless a high torque value is given, a sudden variation in the torque

  appears when switching between communication systems

  This is why a correction is made.

  correction processor K 4 at this instant is K 4 = V / VC <1

  corrected FS slip frequency has a value of

  below the reference slip frequency FSP Therefore, the current I also becomes low As the control system is controlled so that the current I becomes equal to the current control IP, the current AI gap increases and the voltage V increases in

function of the AI difference of the current.

  If the slip frequency Fs used for

  correct the torque reduction associated with a time difference

  varies sharply, there is a sudden variation in the torque, similar to that obtained during the

  switching between control systems.

  FIG. 18 shows the variation of the torque TRQ and the variation of the sliding frequency FS in the case where the current temperature T is lower than the reference temperature To In the example shown, when the frequency FS of the motor is equal at about 2 Hz,

  a correction factor is calculated in such a way that

  mutation between control systems must be carried out with an interval of time or a delay

  up to the moment of switching (4 Hz in this case)

  by a delay circuit 32 In accordance with the

  In this embodiment, a device can be

  tif, in which there is no variation in torque when switching, without adding any new components

  such as a temperature sensor.

  Another embodiment will be explained with reference to FIG. 16. In FIG. 16, the same reference numbers as those used in FIG. 15 denote the same parts or components as those

shown in Figure 15.

  The arrangement of FIG. 16 differs from that of FIG. 15 in that the voltage V of the motor is detected.

  by a detector 31 of the line voltage of the motor to

  duction and by a detector 30 of the motor voltage.

  In this respect, the motor voltage varies in a range from 0 V to 1500 V.

  the control of the voltage VC is between 0 V and

  50 V and a variation of the voltage as a function of the temperature is equal to a few volts If the detectors and 31 are detectors having a caliber of 1500 V or more, it is difficult to measure a voltage variation of a few volts However , if the detectors 30 and 31 are detectors having a range, in which the voltage obtained during the switching from the control of the voltage VC to the control of the frequency FS, is chosen as the maximum voltage (for which a certain margin of variation is allowed), it is possible to measure accurately the voltage variation in

temperature function.

  What has been said above is valid from

  similar for a voltage V (or a modulation rate

  y), which is the output signal of the amplifier 19 represented

shown in Figure 15.

  In accordance with the embodiments

  In Figures 15 and 16, it is not necessary to directly measure the temperature using a temperature sensor. It is difficult to connect a temperature sensor inside an engine. Therefore, if one uses temperature sensors, you have to measure the

  surface temperature of the engine and the ambient temperature

  biante to have an accurate estimate of the temperature

  internal control of each engine In the present forms of

  it is not necessary to measure beforehand

temperatures.

Claims (21)

  1 Control device for an induction motor   characterized in that it comprises: an inverter (4) of variable voltage and variable frequency for converting a direct current into an alternating current;   an induction motor (5) controlled by said on-   duleur; means (13) for controlling the frequency of   slip so that the current of said motor to induce become constant;   means (15,16,17; 18) for executing a   to generate a voltage proportional to the frequency of the inverter; and   means (14; 18) for correcting the voltage   proportional to the frequency of the inverter, according to a   internal impedance angle of said induction motor.   2 Control device for an induction motor   according to claim 1, characterized in that   said means of correction include means (1401-1404)   to receive said slip frequency and a frequency   rotation of said induction motor to calculate an impedance angle, and means (1405) for calculating a correction factor according to said angle impedance.   3 Control device for an induction motor   tion according to claim 2, characterized in that the   said means (1405) for calculating the correction factor com-   take means to divide a predetermined value   by a value equal to the sine of said impedance angle.   4 Control device for an induction motor   according to claim 1, characterized in that   said correction means comprise means (1411), in which the value of a correction factor calculated   beforehand according to said angle of impedance is memo-   in accordance with the frequency of the inverter, the   said means delivering said correction factor in   according to the frequency of the inverter.   A control device for an induction motor, characterized in that it comprises: a variable voltage, variable frequency inverter (4) for converting a direct current to an alternating current;   an induction motor (5) controlled by said on-   duleur; means (13) for controlling the frequency of   slip so that the current of said motor to induce   become constant; means (15,16,17) for executing a command so as to produce a voltage proportional to the frequency of the inverter; and   means (14) for correcting the proportional voltage   the frequency of the inverter, according to the   called slip frequency and a rotation frequency said induction motor.   6 Control device for an induction motor   characterized in that it comprises: a variable voltage, variable frequency inverter (4) for converting a direct current to an alternating current;   an induction motor (5) controlled by said on-   duleur; means (13) for controlling the frequency of   slip so that the current of said motor to induce become constant;   means (15,16,17; 18) for executing a   to generate a voltage proportional to the frequency of the inverter; and   means (14; 18) for correcting the voltage   proportional to the frequency of the inverter, according to a   power factor of said induction motor.   7 Control device for an induction motor   according to claim 6, characterized in that said   Power factor is calculated from the said factor   slip rate and a rotation frequency of that induction motor.   8 Control device for an induction motor   characterized in that it comprises: a variable voltage, variable frequency inverter (4) for converting a direct current to an alternating current;   an induction motor (5) controlled by said on-   duleur; means (13) for controlling the frequency of   slip so that the current of said motor to induce   become constant; means (15,16,17) for executing a command so as to produce a voltage proportional to the frequency of the inverter; and   means (14) for correcting the proportional voltage   the frequency of the inverter, depending on the   a power factor calculated from that frequency   slip rate and a rotation frequency of that induction motor.   9 Control device for an induction motor   characterized in that it comprises: a variable voltage, variable frequency inverter (4) for converting a direct current to an alternating current;   an induction motor (5) controlled by said on-   duleur; means (13) for controlling the frequency of   slip so that the current of said motor to induce become constant;   means (15,16,17; 18) for executing a   to generate a voltage proportional to the frequency of the inverter; and   means (14; 18) for correcting the voltage   proportional to the frequency of the inverter, as a function of the sine of a phase difference between said voltage and the current of said induction motor.   Control device for an ignition motor   duction, characterized in that it comprises: an inverter (4) with variable voltage and variable frequency for converting a direct current into an alternating current;   an induction motor (5) controlled by said on-   duleur; means (13) for controlling the frequency of   slip so that a current of said inductive motor   become constant; and means (14,15,16,17; 18) for producing a   voltage corrected beforehand according to an angle of   internal pedance of said induction motor, depending on the frequency of the inverter.   11 Control device for an ignition motor   duction, characterized in that it comprises: an inverter (4) with variable voltage and variable frequency for converting a direct current into an alternating current;   an induction motor (5) controlled by said on-   duleur; a voltage control system comprising means (8,9,19) for controlling the output voltage of said inverter so that a current of said induction motor takes a constant value, a temperature sensor (27)   connected to said induction motor, means (22) for   delivering a report of an output signal of said temperature sensor to a predetermined value, and means (24) for correcting the reference slip frequency as a function of said ratio;   a control system of the glide frequency   comprising means (13) for controlling the slip frequency so that the current of said induction motor becomes constant, and means (14,15,16,17; 18) for correcting a voltage proportional to the frequency of the inverter according to an internal impedance angle of said induction motor; and means (25,26) for switching between said voltage control system and said system   of the sliding frequency, when the frequency   rotation of said induction motor takes a variable their predetermined.   12 Control device for an ignition motor   Ducting according to claim 11, characterized in that said means for correcting said voltage as a function of said internal impedance comprise means (1401-1404)   to receive said slip frequency and the frequency   rotation of said induction motor to calculate an impedance angle, and means (1405) for calculating a correction factor as a function of said impedance angle.   13 Control device for an ignition motor   Ducting according to claim 12, characterized in that said means (1405) for calculating the correction factor   include means for dividing a predetermined value   terminated by a sine value of said impedance angle.   14 Control device for an ignition motor   duction according to claim 11, characterized in that   said means for correcting said voltage as a function of   said internal impedance angle comprises means (1411), in which the value of a correction factor calculated in a preliminary manner as a function of said impedance angle is stored according to said frequency of the inverter, said means delivering said factor of   correction according to the frequency of the inverter.   Control device for an ignition motor   duction, characterized in that it comprises: an inverter (4) with variable voltage and variable frequency for converting a direct current into an alternating current;   an induction motor (5) controlled by said on-   duleur; a voltage control system comprising means (8, 9, 19) for controlling the output voltage   said inverter, so that a current of said inverter motor   duction takes a predetermined value, a time sensor   temperature (27) connected to said induction motor, means (22) for outputting a ratio of an output signal of said temperature sensor to a predetermined value, and means (24) for correcting the reference slip frequency based on the said report;   a control system of the glide frequency   comprising means (13) for controlling the slip frequency so that the current of said induction motor becomes constant, and means (14,15,16,17; 18) for correcting a voltage proportional to the frequency of the inverter according to a power factor of said induction motor; and means (25,26) for performing a switch   between said voltage control system and said system   controlling the sliding frequency when the rotation frequency of said induction motor is predetermined value.   16 Control device for an ignition motor   duction, characterized in that it comprises: a variable voltage, variable frequency inverter (4) for converting a direct current into an alternating current;   an induction motor (5) controlled by said on-   duleur; a voltage control system comprising means (8, 9, 19) for controlling the output voltage   said inverter, so that a current of said inverter motor   a predetermined temperature value, a temperature sensor (27) connected to said induction motor, means (22) for outputting a ratio of an output signal of said temperature sensor to a predetermined value, and means (24); ) to correct the reference slip frequency according to said ratio;   a control system of the glide frequency   comprising means (13) for controlling the slip frequency so that the current of said induction motor becomes constant, and means (14,15,16,17; 18) for correcting a voltage proportional to the frequency of the inverter as a function of the sine of a phase difference between said voltage and the current of said induction motor; and means (25,26) for performing a switch   between said voltage control system and said system   controlling the sliding frequency when the rotation frequency of said induction motor is predetermined value.   17 Control device for an ignition motor   duction, characterized in that it comprises: an inverter (4) with variable voltage and variable frequency for converting a direct current into an alternating current;   an induction motor (5) controlled by said on-   duleur; means (8,9,19) for controlling the output voltage of said inverter so that a current of said induction motor takes a predetermined value; means (13) for generating the frequency of   the inverter from a reference slip frequency.   frequency and rotation frequency of said induction motor tion;   means (28) for generating a reset voltage   f erence corresponding to the rotation frequency of the said   induction cooker; and means (24,29) for correcting said frequency   reference slip as a function of an output signal.   of said output voltage control means and of said reference voltage.   18 Control device for an ignition motor   duction, characterized in that it comprises: an inverter (4) with variable voltage and variable frequency for converting a direct current into an alternating current;   an induction motor (5) controlled by said on-   duleur; a voltage control system comprising means (8, 9, 19) for controlling the output voltage   said inverter so that a current of said inverter motor   a predetermined value, means (28) for producing a reference voltage corresponding to the rotation frequency of said induction motor, and means (24,29) for correcting the reference slip frequency as a function of the output signal. said means for controlling the output voltage and said reference voltage;   a control system of the glide frequency   comprising means (13) for controlling the slip frequency so that the current of said induction motor becomes constant, and means (14,15,16,17; 18) for correcting a voltage proportional to the frequency of the inverter according to an internal impedance angle of said induction motor; and means (25,26) for performing a switch   between said voltage control system and said system   controlling the sliding frequency when the rotation frequency of said induction motor is predetermined value.   19 Control device for an ignition motor   duction according to claim 18, characterized in that   said means for correcting said voltage as a function of   said internal impedance angle include means (1401-   1404) for receiving said slip frequency and the   rotation frequency of said induction motor for   angle of impedance, and means (1405) for calculating   allocate a correction factor according to said impedance angle.   Control device for an ignition motor   Ducting according to claim 19, characterized in that said means (1405) for calculating the correction factor   include means for dividing a predetermined value   born by a sine value of said impedance angle.   21 Control device for an ignition motor   duction according to claim 18, characterized in that   said means for correcting said voltage as a function of   said internal impedance angle comprises means (1411), in which the value of a correction factor previously calculated as a function of said impedance angle is stored as a function of said frequency of the inverter and which delivers said correction factor in terms of the frequency of the inverter.   22 Control device for an ignition motor   duction, characterized in that it comprises: an inverter (4) with variable voltage and variable frequency for converting a direct current into an alternating current;   an induction motor (5) controlled by said on-   duleur; a voltage control system comprising means (8, 9, 19) for controlling the output voltage   said inverter so that a current of said inverter motor   a predetermined value, means (28) for producing a reference voltage corresponding to the rotation frequency of said induction motor, and means (24,29) for correcting the reference slip frequency as a function of a signal. outputting said output voltage control means and said reference voltage;   a control system of the glide frequency   including means (13) for controlling a frequency   slip so that the current of said induction motor becomes constant, and means (14,15,16,17; 18) for correcting a voltage proportional to the frequency of the inverter as a function of a power factor of said induction motor; and means (25,26) for performing a switch   between said voltage control system and said system   controlling the sliding frequency when the rotation frequency of said induction motor is predetermined value.   23 Control device for an ignition motor   duction, characterized in that it comprises: an inverter (4) with variable voltage and variable frequency for converting a direct current into an alternating current;   an induction motor (5) controlled by said on-   duleur; a voltage control system comprising means (8, 9, 19) for controlling an output voltage   said inverter so that a current of said inverter motor   a predetermined value, means (28) for producing a reference voltage corresponding to the rotation frequency of said induction motor, and means (24,29) for correcting the reference slip frequency as a function of a voltage. input of said induction motor and said reference voltage;   a control system of the glide frequency   comprising means (13) for controlling the slip frequency so that the current of said induction motor becomes constant, and means (14,15,16,17; 18) for correcting a voltage proportional to the frequency of the inverter as a function of the sine of a phase difference between said voltage and the current of said induction motor; and means (25,26) for performing a switch   between said voltage control system and said system   controlling the sliding frequency when the rotation frequency of said induction motor is predetermined value.   24 Control device for an ignition motor   duction according to any of the claims   (18, 22, 23), characterized in that said means (24, 29) for correcting the reference slip frequency are equipped with means (32) for effecting the transition from a slip frequency before correction to a frequency of   slip after correction with a predetermined delay.   A method for producing a voltage profile corresponding to the frequency of a variable voltage, variable frequency inverter (4) which controls an induction motor (5), characterized in that a profile, for which the ratio of the voltage at the frequency is constant, is multiplied by a correction factor corresponding to an internal impedance angle of said induction motor for   produce said voltage profile corresponding to the frequency quence of said inverter.   26 Control device for an ignition motor   duction, characterized in that it comprises: an inverter (4) with variable voltage and variable frequency for converting a direct current into an alternating current;   an induction motor (5) controlled by said on-   duleur; means (13) for controlling the frequency of   slip so that a current of said inductive motor become constant;   means (15, 16, 17, 18) for applying a   to generate a voltage proportional to the frequency of the inverter; and means (14; 18) for correcting said voltage proportional to the frequency of the inverter as a function of a power factor of said induction motor, which makes it possible to perform a control such as the torque of said   induction motor becomes constant.